10-20 WHP max with a custom tune... Gonna need some more supporting mods (exhaust) or a bolt-on supercharger to see any noticeable gains

Do the older model DME's adjust at all for octane changes at all ?

I had heard on the other end of the scale that the DME would pull timing if on N20 and detonation conditions were detected....

Maybe it was just that great smelling MS109 that affected my head but the times I was doing with the high octane and by just adding a CAI (AFE) and cleaning injectors, intakes etc was quite a bit better

I had heard on the other end of the scale that the DME would pull timing if on N20 and detonation conditions were detected....

I would assume that older DMEs would only retard timing (like the newer BMW DMEs on the 135/335/M3/etc etc), but they would never advance it beyond the factory timing target. Just means if you put 100+ octane in the car, it would run like it's supposed to but not any stronger.

The older ECUs can adv/retard timing depending on the maps available... at least 2: low and high octane. The switch is based on knock sensor activity. The newer BMW DME only has 1 timing curve and just continually retards/advances real time, but wont adv past the set curve. Likely the power difference you felt is jumping to a higher oct map.

The older ECUs can adv/retard timing depending on the maps available... at least 2: low and high octane. The switch is based on knock sensor activity. The newer BMW DME only has 1 timing curve and just continually retards/advances real time, but wont adv past the set curve. Likely the power difference you felt is jumping to a higher oct map.

Not that I don't believe you, or the other 100 people that have said this on the internet. But for my E46 M3, I am trying to find anything that shows the DME can adjust for higher octane levels.

IF it was up to me, I'd aim for a 95 octane tune vs. a 93 --- Reason why is you're already going through all the trouble of blending fuels, so why not turn it up just a bit more. Still won't require you run straight 100+, but the gains will be more "pronounced" in a 91/95 tune vs 91/93.

Race gas naturally retards the peak cylinder pressure event. It burns slower and more controlled. Therefore adding race gas to a car that is tuned for 93 will in theory make less power.
110 octane fuel usually needs a 4 degree advance in timing globally across the ignition map to achieve the same peak cylinder pressure timing that the car was tuned for on 93.
the only circumstance where race fuel would yield more power without any other changes whatsoever is in the circumstance where the car actually needed less timing in order to achieve Maximum Brake Torque.
I.e.- a engine that is moving air much more efficiently after modifications will generally require less ignition advance to achieve MBT.

4deg is a bunch for newer engines... maybe on a hemi. MBT is typically knock limited, no way you can be past theoretical MBT (ie peak pressure <15deg ATDC) on pump with a S motor. Added power is due to more ign adv... either by reduced knock retard or jumping to a more aggressive ign map putting you closer to optimum peak pressure of 15-18deg.

All race gas does not necessarily burn slower... depends on the gas/additives. The primary advantage is higher auto ignition temp.

Race gas naturally retards the peak cylinder pressure event. It burns slower and more controlled. Therefore adding race gas to a car that is tuned for 93 will in theory make less power.
110 octane fuel usually needs a 4 degree advance in timing globally across the ignition map to achieve the same peak cylinder pressure timing that the car was tuned for on 93.
the only circumstance where race fuel would yield more power without any other changes whatsoever is in the circumstance where the car actually needed less timing in order to achieve Maximum Brake Torque.
I.e.- a engine that is moving air much more efficiently after modifications will generally require less ignition advance to achieve MBT.

- calorific value of the fuel to consider (heat release per unit mass)

- latent heat of vaporization. some fuels can increase power is if they take heat away from the intake charge lowering the IAT and thus increasing VE. ethanol, methanol and such fuels this effect is more pronounced.

also a more oxygenated fuel can make more power, and due to the environmentalists and those concerned with life of catalytic converters and o2 sensors means that pump fuel doesn't have some additives that can improve performance.

one things is that simply looking at the Octane and ignition timing is really only one part of story. the chemistry and thermodynamics is complex